U.S. patent number 4,289,797 [Application Number 06/083,902] was granted by the patent office on 1981-09-15 for method of depositing uniform films of si.sub.x n.sub.y or si.sub.x o.sub.y in a plasma reactor.
This patent grant is currently assigned to Western Electric Co., Incorporated. Invention is credited to Aline Akselrad.
United States Patent |
4,289,797 |
Akselrad |
September 15, 1981 |
Method of depositing uniform films of Si.sub.x N.sub.y or Si.sub.x
O.sub.y in a plasma reactor
Abstract
A method of depositing a uniform dielectric film on a silicon
substrate comprising flowing a plasma comprising an RF-excited
mixture of an inert gas such as argon and silane over the substrate
to form a film of porous a-Si.sub.x H.sub.y over the surface of the
substrate. The flow of plasma is then discontinued and a flow of a
nitrogen or oxygen plasma is substituted therefor. The temperature
of the substrate is increased to at least 360.degree. C. to
diffuse-out hydrogen from the Si.sub.x H.sub.y film on the
substrate, each departing hydrogen atom leaving a dangling Si bond
behind which combines with the activated oxygen or nitrogen thereby
to form the desired dielectric film of formula Si.sub.x N.sub.y or
Si.sub.x O.sub.y.
Inventors: |
Akselrad; Aline (Princeton,
NJ) |
Assignee: |
Western Electric Co.,
Incorporated (New York, NY)
|
Family
ID: |
22181388 |
Appl.
No.: |
06/083,902 |
Filed: |
October 11, 1979 |
Current U.S.
Class: |
427/539;
118/50.1; 204/164; 427/573; 427/578 |
Current CPC
Class: |
C23C
16/56 (20130101); C23C 16/505 (20130101) |
Current International
Class: |
C23C
16/56 (20060101); C23C 16/505 (20060101); C23C
16/50 (20060101); C23C 011/00 () |
Field of
Search: |
;427/38,39,40 ;204/164
;118/723,50.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Rosler et al., "Solid State Technology", Jun. 1976, pp. 45-50.
.
Taft, "J. Electrochem. Soc.: Solid State Science", vol. 118, No. 8,
Aug. 1971, pp. 1341-1346. .
Brodsky, "IBM TDB", vol. 19, No. 11, Apr. 1977, pp.
4447-4450..
|
Primary Examiner: Newsome; John H.
Attorney, Agent or Firm: Spivak; J. F.
Claims
What is claimed is:
1. A method of depositing a uniform dielectric film on a silicon
substrate, comprising the steps of:
flowing a first plasma comprising an excited mixture of inert gas
and a volatile Si compound over said substrate thereby to form a
film having porous a-Si.sub.x H.sub.y over the surface of said
substrate;
discontinuing the flow of said first plasma and substituting
therefor a flow of a second excited plasma comprising an activated
gas selected from the group consisting of oxygen and nitrogen over
said substrate; and then
elevating the temperature of said substrate to cause the hydrogen
to diffuse-out from said porous a-Si.sub.x H.sub.y film, each
departing hydrogen atom leaving behind a dangling Si bond which
combines with an excited radical of the activated gas in said
second plasma thereby to form said dielectric film of formula
Si.sub.x M.sub.y, where M represents either oxygen or nitrogen,
depending on the identity of said activated gas.
2. The method according to claim 1, wherein said substrate is
physically located within an RF-excited, plasma reaction chamber
and the gas which comprises said second excited plasma is activated
by increasing the level of the RF power supplied to the reaction
chamber over that which was supplied to excite the mixture of the
inert gas and the volatile Si compound.
3. The method according to claim 1, wherein said substrate is
physically positioned within an RF-excited, plasma reaction chamber
and the gas which comprises the second excited plasma is activated
by changing the frequency of the RF-excitation to a frequency which
is above that used to excite the mixture of the inert gas and the
volatile Si compound.
4. The method according to claim 1, wherein said substrate is
physically positioned within a plasma reaction chamber and the gas
which comprises the second excited plasma is activated by adjusting
the pressure of the gas which comprises the second excited plasma
to a value to permit activation.
5. The method according to claim 1, wherein said substituting step
comprises:
substituting the flow of a second excited plasma comprising a
mixture of activated oxygen and nitrogen, whereby the dielectric
film formed on said substrate comprises Si.sub.x N.sub.y
O.sub.z.
6. The method according to claim 1, wherein said
temperature-elevating step comprises raising the temperature of
said substrate in excess of 360.degree. C.
Description
TECHNICAL FIELD
Broadly speaking, this invention relates to plasma deposition. More
particularly, in a preferred embodiment, this invention relates to
a method of depositing a two-component film of material from
successive, one-component gas plasmas.
BACKGROUND OF THE INVENTION
Plasma deposition is a technique that is widely used in industry to
deposit thin films of material on a variety of workpieces. For
example, in the manufacture of integrated circuits, an RF-excited
plasma comprising an inert gas, such as argon, and the reactive
species silane, (SiH.sub.4,) and ammonia, (NH.sub.3,) is used to
deposit a thin film of SiN, the designation given to compositions
approaching Si.sub.3 N.sub.4 but not necessarily identical with
Si.sub.3 N.sub.4, on a silicon wafer approximately 3 inches in
diameter. The SiN film can then be used as mechanical protection
during subsequent processing of the wafer, as a dielectric
insulating layer between 2 layers of metallization, or (if
improved) as a hermetic seal.
It will be appreciated that among the desirable properties that
must be possessed by such a silicon nitride film are uniformity of
thickness, uniformity of composition and freedom from defects such
as impurities and pin-holes. Unfortunately, the prior art plasma
deposition processes are unpredictable and such undesirable defects
are quite common, occurring randomly, for no apparent reason.
One mechanism that has been proposed to explain at least some of
the observed defects is a reaction of the form:
where
4 4 and m.ltoreq.3,
where * indicates some metastable excited configuration and where
the component Si.sub.x N.sub.y H.sub.z can be in an excited state
or in a ground state, the said reaction taking place in the plasma
rather than on the surface of the substrate.
As might be expected, such a reaction would produce particulate
matter that would deposit onto the surface of the substrate. One
reason that has been suggested for the occurrence of this reaction
is that, once a molecule of Si.sub.x N.sub.y H.sub.z has formed in
the plama, it provides all of the incentives for plasma deposition
that the substrate itself provides.
SUMMARY OF THE INVENTION
As a solution to this problem, I propose a method wherein a thin,
uniform film of porous a-Si.sub.x H.sub.y is deposited on a silicon
substrate by means of a one-component plasma comprising a
silicon-containing active radical, such as silane or silicon
tetrachloride. After the porous film has been deposited, this
one-component plasma is withdrawn and the film oxidized or nitrided
in situ by flowing activated oxygen or nitrogen over the
substrate.
The invention and its mode of operation will be more fully
understood from the following detailed description.
DETAILED DESCRIPTION
The instant invention provides for the plasma deposition of denser,
and more uniform films of Si.sub.x N.sub.y, Si.sub.x N.sub.y
O.sub.z or Si.sub.x O.sub.y in a two-step process utilizing
successive one-component plasmas.
As an example, consider the deposition of Si.sub.x N.sub.y. First,
using an entirely conventional Reinberg-type plasma reaction
chamber, or equivalent, a thin, uniform film of Si.sub.x H.sub.y is
deposited on a silicon substrate using an RF-excited SiH.sub.y +Ar
gas plasma. The Reinberg reaction chamber is described in U.S. Pat.
No. 3,757,733 which issued on Sept. 11, 1973 to A. R. Reinberg,
which patent is hereby incorporated by reference as if more fully
set forth herein. The ratio of y/x in the deposited Si.sub.x
H.sub.y film is adjusted by controlling the temperature of the
substrate, which will typically fall between 50.degree. C. and
300.degree. C.
The Si.sub.x H.sub.y film that is deposited is actually a porous,
amorphous a-Si.sub.x H.sub.y film with its porosity and total
hydrogen content being primarily determined by deposition
temperature, deposition rate and the RF power which is applied to
the reaction chamber. The properties of thin films of a Si.sub.x
H.sub.y are described in "Infrared and Raman Spectra of the
Silicon-Hydrogen Bonds in Amorphous Silicon Prepared by Glow
Discharge and Sputtering" by M. H. Brodsky, M. Cardona and J. J.
Cuomo, Phy. Rev. B., Vol. 16, No. 8, 15 October 1977 at Pg. 3556;
"Properties of Amorphous Silicon and a-Si Solar Cells" by D. E.
Carlson, C. R. Wronski, J. I. Pankove, P. J. Zanzucchi and D. L.
Staebler, RCA REview, Vol. 38, June 1977, pp. 211-225 (Table I at
Pg. 217 in particular); and "Controlling the Type of Bonded
Hydrogen Sites in Glow-Discharge Amorphous Silicon Films" by M. H.
Brodsky, IBM Technical Disclosure Bulletin, Vol. 19, No. 11, April
1977, pp. 4447-4450, all of which references are hereby
incorporated by reference as if more fully set forth herein.
After an appropriate time interval, the flow of SiH.sub.4 +Ar is
replaced by a flow of N.sub.2, or other suitable
nitrogen-containing mixture.
Because the flow of SiH.sub.4 has been terminated, its premature
decomposition is no longer a problem; thus, the pressure, the
frequency of the RF-excitation and/or the input power to the
reaction chamber may be increased to a point where activated
nitrogen is produced in the chamber. Next, the temperature of the
substrate is raised to more than 360.degree. C. so that hydrogen
starts to diffuse out of the Si.sub.x H.sub.y. Since a-Si is
porous, and since the departing hydrogen leaves behind dangling Si
bonds, the diffusion of activated N into Si and the formation of
Si-N bonds is accelerated, thus forming a uniform, impurity-free,
dielectric film of Si.sub.x N.sub.y.
If extremely uniform layers of Si.sub.x N.sub.y are required, the
process may be modified by laying down a very thin layer of
a-Si.sub.x H.sub.y and repeating the procedure several times until
the desired overall thickness is obtained. As an alternative, one
could start the process by depositing a thin layer of Si.sub.x
N.sub.y H.sub.z which is porous and N-deficient and complete the
nitridation in a N* rich plasma by adding some nitrogen-containing
compound to the initial gas plasma. However, the possibility of
non-uniformity remains with this alternate embodiment.
The above-described process has the following advantages:
1. In a simple plasma reactor, the uniformity of a one-component
film, such as Si, is more easy to obtain than the uniformity of a
film which is deposited from a mixture of two gases which differ in
activation energy, for example, SiH.sub.4 and N.sub.2 or SiH.sub.4
and NH.sub.3 ;
2. More complex compositions and layer structures can be attempted
sequentially;
3. If the diffusion of the active radical (N*) into Si layer
dominates, the film will be denser than ordinary SiN and it is
possible that the tensile stress will decrease; and
4. Homogenous nucleation of Si.sub.x N.sub.y H.sub.z and the
resulting particle contamination are eliminated.
One skilled in the art will appreciate that, by substituting a flow
of activated oxygen for the flow of activated nitrogen in the
above-described process, the film that would ultimately form on the
substrate would be Si.sub.x O.sub.y rather than Si.sub.x N.sub.y.
Similiarly, by flowing simultaneously both nitrogen and oxygen, the
film would comprise Si.sub.x N.sub.y O.sub.z. It will also be
appreciated that while RF-excitation of the plasma is the preferred
embodiment, other forms of excitation are possible. Likewise, while
silane is the preferred embodiment for the first plasma, other
volatile Si compounds can be used.
One skilled in the art may make various changes to the
above-described processes without departing from the spirit and
scope of the invention.
* * * * *